Bobbin-thread cases



April 17, 1956 J. P. ENOS 2,742,008

BOBBIN-THREAD CASES Filed June 15, 1953 INVENTOR. W John P. Enos WITNESS 4 y wks c ju ATTDRNEY United States Patent 2,742,008 BOBBIN-THREAD CASES,

Application June 15, 1953, Serial No. 361,648 2 Claims. (Cl. 112--229) This invention relates to sewing machines of the lock stitch type provided with a bobbin and bobbin case for holding thread and more particularly relates to bobbinthread tensioning means.

It is an object of this invention to provide a bobbin case for a lock-stitch sewing machine having adjustable tension means for the bobbin thread.

, It is a further object of the invention to provide a bobbin-thread tensioning means which is quickly adjustable to accommodate different sizes of thread.

With the above and other objects in view, the invention comprises 'the devices, combinations and arrangements of parts hereinafter set forth and illustrated in the accompanying drawings of a preferred embodiment of the invention and the advantages attained thereby will be readily apparent to those skilled in the art.

In the drawings, Fig. 1 is a front elevational view of a bobbin-thread case embodying the invention.

Fig. 2 is an enlarged front elevational view of a portion of the bobbin-thread case shown in Fig. 1.

Fig. 3 is an enlarged sectional view taken substantially on line 33 of Fig. 2.

Fig. 4 is a disassembled perspective view of the tension spring and tension adjusting means.

Fig. 5 is a right side elevational view of a portion of the thread-case and tension spring shown in Fig. 1 showing the primary tension adjusting screw.

Referring more particularly to the drawings, a conventional sewing machine throat-plate is shown in Fig. 1 with a loop-taker 11 located directly below the throat-plate 10. The loop-taker is provided with a loop seizing beak 12 and a heel 13. A thread case 14 is supported by the loop-taker 11 and carries a thread-tension spring 15 which is generally similar to the tension spring structure shown in the Barron U. S. Patent No. 1,879,023, dated Sept. 27, 1932. The thread case 14 comprises a cylindrical shell having a substantially cylindrical wall portion 16 closed at one end by an end wall 17 and adapted to receive a conventional bobbin of under-thread, as shown in the said Barron patent. The thread case 14 is supported on a central bobbin-post 18 fastened to the looptaker 11. A retaining finger 19 carried by the thread case 14 extends between two stationary fingers 20 which prevent the thread case 14 from rotating with the loop-taker 11. The thread tension spring 15 is curved and fitted to the outer cylindrical surface of the thread case 14, but the radius of curvature of the spring 15 is less than the radius of curvature of the cylindrical thread case wall portion 16. The spring 15 is formed with a tail 21 which extends into a positioning hole 22 formed in the wall portion 16.

A primary tension adjusting screw 23 passes through a hole 24 formed in the spring 15 and is threaded into the wall portion 16 of the thread case 14. A fiat 25 is formed on the wall portion 16 under the free end of the tension spring 15. An annular ridge 26 is formed around the hole 24 in the tension spring 15 and is impressed with indicia marks 27. A slot 28 in the head of the adjusting screw 23 coacts with the indicia marks 27 to form a tension indicator.

A notch 29 is formed in the end wall 17 of the case 14 to receive two ear-portions 30 and 31 formed on the spring 15 and extending substantially parallel to the end wall 17. The ear portions 30 and 31 form a threadguiding notch 32 between them. A guide-slot 33 in the end wall 17 intersects the notch 29 and forms a guideway for a secondary tension adjusting member or slide 34. The slide 34 is provided with a slot through which passes a clamping screw 35 threaded into the end wall. A tang 36 formed on the slide 34 is bent into the notch 29 and is engageable with a similar tang 37 formed on the spring ear-portion 30. Under-thread 38 from the interior of the case 14 extends through a hole 39 in the case 14, between the cylindrical wall'16 and the spring 15 and between the spring ear-portions 30 and 31.

It is believed that with the above description in view, the operation and advantages of the device will be readily understood. For normal sewing with average sized thread used in thethread-case 14, the slide 34 is retracted in the slideway 33 to a position where it does not engage the tang 37 of the spring 15. Under these conditions, the thread tension is changed only by the primary adjusting screw 23. Sincethe fiat 25 is positioned under the tension end of the. spring 15, contact is always assured between the spring 15 and the thread case 14 only at the edge of the fiat 25. The force exerted by the spring 15 can be varied by turning the adjusting screw 23. Thus, when the thread 38 is drawn between the spring 15 and the thread case 14, the screw 23 is turned until the desired tension is obtained on the thread 38. It will be appreciated that the range of tension adjustments obtainable with the primary adjusting screw alone is limited. If a very light tension is required on a thread of large diameter, the adjusting screw 23 cannot be backed out far enough to relieve the tension sufliciently, since its length is limited by the thickness of the cylindrical wall portion 16. Thus, in order to provide a wider range of tension adjustment, the slide member 34 is provided. In many types of sewing, such as darning and embroidering, it is desirable to use heavy, large diameter bobbin-thread in the thread case 14 under relatively light tension. Further, it is desirable to obtain the proper tension on the heavier thread without changing the adjustment of the primary adjusting screw 23 from its adjusted position for applying the proper tension to thread of small diameter used for normal sewing. The thread tension on small diameter thread for normal sewing is adjusted with the slide 34 retracted against the end wall of the slideway 33 out of contact with the tang 37. The only adjustment which affects the thread tension under these conditions is the primary adjusting screw 23 which can be turned until the proper tension is obtained on the thread 38. When it is desired to sew with an extremely heavy thread, the thread is drawn under the spring 15, as shown in the drawing, without disturbing the adjustment of the primary adjusting screw 23. With the thread in sewing position, the screw 35 is loosened and the slide 34 moved outwardly until it engages the tang 37 of the spring 15 and raises the spring 15 far enough to relieve the pressure on the thread and obtain the proper thread tension. The screw 35 is then retightened to hold the slide in place. Normally, the proper thread tension for large diameter thread is obtained merely by moving the slide 34 without disturbing the adjustment of the primary adjusting screw 23. However, if sufficient adjustment cannot be obtained by moving the slide 34, the position of the slot 28 of the adjusting screw 23 relative to the indicia marks 27 can be noted and the adjusting screw can then be turned to obtain a new range of adjustment for the slide 34 and the thread tension. When it is desired to return the thread tension to the proper tension for small diameter thread required for normal sewing, it is only necessary to release the slide 34 and move it back in the slideway out of engagement with the tang 37. If the primary adjusting screw has been moved, it is also necessary to move it back to the position with respect to the indicia marks 27 which it initially occupied.

From the foregoing description, it is apparent that the improved thread case provides a convenient means for changing the tension on the under-thread of a sewing machine over a wide range to accommodate a wide range of thread diameters. Further, the tension device provides a means for quickly returning the under-thread tension to that required for small diameter thread after sewing requiring a large diameter thread is completed.

Having thus set forth the nature of the invention, what I claim herein is:

l. A bobbin-thread case having a substantially cylindrical shell and an end wall closing one end of said shell,

a thread-ter1sion leaf-spring applied to the outer surface of said shell, said spring having an unflexcd radius of curvature less than the radius of curvature of said cylindrical shell, a primary tension adjusting screw passing through said spring at one extremity thereof and threaded into said cylindrical shell, a guide slot formed in said end wall, a secondary tension-adjusting slide member positioned in said slot for sliding movement, said slide memher having a tang formed thereon, thread-guide ear-portions formed on said tension spring at the extremity opposite that through which said primary tension-adjusting Cil 4 it screw passes, said ear portions extending along said end wall, one of said ear-portions having a tang formed thereon, said tangs being engageable with each other to move one end of said spring away from said shell and means for securing said slide member to said end wall.

2. A bobbin-thread case having a substantially cylindrical shell and an end wall closing one end of said shell, a thread-tension leaf-spring applied to and pressing at one extremity against the outer surface of said shell, said spring extremity and said shell defining opposed threadtensioning jaws, said spring having an unflexed radius of curvature less than the radius of curvature of said shell, a primary tension-adjusting screw threaded into said cylindrical shell and disposed at the extremity of said spring opposite said thread-tensioning jaws and in engagement with that side of said spring opposite said shell, said screw being adapted to increase the pressure of said spring against said shell, and a secondary tensioning adjusting device carried by one of said thread-tensioning jaws and extending between said spring and said shell to relieve the pressure applied by said primary tension ad justing screw.

References Cited in the file of this patent UNITED STATES PATENTS 2,034,506 Colegrove et al. Mar. 17, 1936 2,299,524 Chas'on Oct. 20, 1942 2,327,817 Parry Aug. 24, 1943 2,488,052 Casas Robert Nov. 15, 1949 

